The present invention relates to electromagnetic devices, and more particularly, to inductors.
A high power converter application, such as a PWM-based uninterruptible power supply (UPS), may require low inductance/high current inductors for power conversion circuits, such as rectifiers and inverters. In such an application, it may be desirable to maintain useful inductance to ˜3 times rms rated current. Operational currents may include both a 50/60 Hz power component and high frequency ripple currents.
Conventional inductor designs include closed flux path and gapped (discrete & distributed) core designs. Torroidal designs may require a complex winding design, and core heat may be trapped inside such a complex winding. Winding heat may further add to core temperature, and inner winding layers may be difficult to keep cool in such designs. Gapped EE/EI or UU/UI designs often include a large core volume with a large air gap. Difficulties in cooling often drives toward the use of a ferrite core, which may be costly due to higher core volume.
Open flux path (e.g., air core) inductors may also be used. Simple air core designs may occupy a large volume to achieve a desired inductance, which can lead to high coil resistance and losses. Multiple layers can amplify skin and proximity effect losses and can impede cooling of inner layers. Losses often exceed acceptable levels, and the return flux path (thru surrounding air) may adversely affect nearby items. Escaping radiated fields may elevate EMI levels, and adjacent sensitive electronic circuits may respond adversely to this EMI.